1. Field of the Invention
This invention relates to self-propelled straddle carrier type material handling vehicles so designed that the load to be carried is suspended within the framework of the vehicle, the vehicle may be of such size and proportions as to permit engaging, hoisting, stacking, and transporting van size containers by driving the vehicle over them from either direction.
2. Discussion of the Prior Art
Prior art machines of the above type are subject to heavy wheel loadings, uneven weight distribution among the supporting wheels and poorly coordinated steering, which results in excessive tire maintenance and damage to the surfaces upon which they operate. Further, their exposed bearings and linkage wear rapidly requiring frequent lubrication and replacement.
A straddle crane, which has been reduced in width, is disclosed in U.S. Pat. No. 3,804,189, the crane having four wheels on each side where the inner wheels are sprung and the outer wheels are unsprung, the sprung wheels being suspended by rubber enclosed compressed air suspension units. In a straddle crane, the arches are the dominant feature and are connected by flexible side frame members. There are no springs and the frames flex with the contour of the supporting surface. This means the load bay is distorted which in turn brings on numerous other complications. The frame of a straddle carrier such as that of the present invention is as rigid as practical and the machine is supported by some form of flexible suspension system. The machines do not flex to follow the contours of the supporting surface. Other prior art straddle carrier patents are my U.S. Pat. Nos. 3,655,081 and 3,703,243, both of which are hereby incorporated herein by reference.